Toshiba TV29C90 problem; Image fades to black...

[Louie]

thanks, Sam, you've been a great help to me on many occasions. basically
it comes down to the KA2915 chip itself. i looked at the
chipdoc

http://asu.info.kuzbass.net/documentation/pdf/k/ka2915.pdf
or
http://www.elektro-obecnice.cz/data/pdf/ka/ka2915.pdf

and it looks like the chip is designed to accept external sync and
horizontal and vertical oscillation and external audio RF. but i can't
tell if it can accept external composite video. maybe it does and i
could just filter the composite and put it at pins 14 and 15. anyway
this is my theory.

Louie

 

[mike]

Jeremy wrote:

The one I picked up (BK Precision 881) claims to output @ 15mV and
came out June 30, 2003, so it's fairly new. I'm wondering if it's a
bad tester because it can't seem to read ESR correctly in-circuit.

Jeremy

Typically, ESR is not a problem in a high impedance circuit.

ESR is often a problem in a low impedance circuit...like a power supply.
If you have a bunch of caps in parallel, the ESR meter can't tell which
if any are bad. Other stuff in the circuit makes it worse.
I've had zero success with ESR measurements in circuit. The only place
it works is where there's only one cap that could be removed easily for
testing. And that's happened...well...never.
mike




--
Bunch of stuff For Sale and Wanted at the link below.
laptops and parts Test Equipment
4in/400Wout ham linear amp.
Honda CB-125S
400cc Dirt Bike 2003 miles $450
Police Scanner, Color LCD overhead projector
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/

 

[Jim Thompson]

On Tue, 02 Sep 2003 22:43:41 +0200, Zak <Zak@spam.invalid> wrote:

Jim Thompson wrote:

When we returned she told us that, when using our shower, it sometimes
felt like an electrical shock.

A little metering revealed 15VAC between the shower head and the
drain.

In Arizona "ground" is established by bonding water pipes to incoming
neutral (but not the sewer piping).

Aagh!

Around here (Netherlands) ground and neutral are totally different
things. Consumers are not supposed to be interested in which of the plug
pins is neutral; could even be 2 x 115 volts in some places.

The installer is supposed to know what is hot - that's the side the
light switch goes on.

Still goes wrongs sometimes: last case making the paper was a 'ring
ground' connecting different houses to a single ground pen someplace -
which had failed.

Then there's folks putting a srew from the lamp fixture below into a
shower drain, causing leak, wetness, and leakage. Not good.

OTOH all metal objects in bathroom space need to be wired together in a
way that is easy to inspect - at least for newly built homes.

Connecting ground to water is also not allowed for new buidings. A
separate ground pin in the earth, wired to a separate net in the home,
is what it should be. Never connected to neutral.

Where do people connect neutral to ground by design?


Thomas

I think I've confused you with neutral, which around here is supposed
to be "ground". Then there's "common" which is like ground but not
connected to ground ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Jim Thompson]

On Tue, 02 Sep 2003 13:47:25 -0700, Jim Thompson
<Jim-T@golana-will-get-you.com> wrote:

On Tue, 02 Sep 2003 22:43:41 +0200, Zak <Zak@spam.invalid> wrote:

Jim Thompson wrote:

When we returned she told us that, when using our shower, it sometimes
felt like an electrical shock.

A little metering revealed 15VAC between the shower head and the
drain.

In Arizona "ground" is established by bonding water pipes to incoming
neutral (but not the sewer piping).

Aagh!

Around here (Netherlands) ground and neutral are totally different
things. Consumers are not supposed to be interested in which of the plug
pins is neutral; could even be 2 x 115 volts in some places.

The installer is supposed to know what is hot - that's the side the
light switch goes on.

Still goes wrongs sometimes: last case making the paper was a 'ring
ground' connecting different houses to a single ground pen someplace -
which had failed.

Then there's folks putting a srew from the lamp fixture below into a
shower drain, causing leak, wetness, and leakage. Not good.

OTOH all metal objects in bathroom space need to be wired together in a
way that is easy to inspect - at least for newly built homes.

Connecting ground to water is also not allowed for new buidings. A
separate ground pin in the earth, wired to a separate net in the home,
is what it should be. Never connected to neutral.

Where do people connect neutral to ground by design?


Thomas

I think I've confused you with neutral, which around here is supposed
to be "ground". Then there's "common" which is like ground but not
connected to ground ;-)

...Jim Thompson

And I should have added, "earth" is Arizona is not adequate to call
ground... the water table is several hundred feet down :-(

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Tweetldee]

"Louie" <beavisnbutthead@softhome.net> wrote in message
news:UM55b.333837$o%2.153601@sccrnsc02...

thanks, Sam, you've been a great help to me on many occasions. basically
it comes down to the KA2915 chip itself. i looked at the
chipdoc

http://asu.info.kuzbass.net/documentation/pdf/k/ka2915.pdf
or
http://www.elektro-obecnice.cz/data/pdf/ka/ka2915.pdf

and it looks like the chip is designed to accept external sync and
horizontal and vertical oscillation and external audio RF. but i can't
tell if it can accept external composite video. maybe it does and i
could just filter the composite and put it at pins 14 and 15. anyway
this is my theory.

Louie

Louie,
Looks like composite video is developed inside the IC, and is available at
pin 5. From there, it goes thru a filter of sorts and is then fed back into
the sync separator to extract and shape the sync pulses. Pin 5 contains
both video and sound. But the sound is still at the sound IF, which is sent
thru a BP filter to strip off the video before it is sent into the sound IF
amp and detector.
I'll bet that if break the circuit at pin 5, and you switch your external
composite video into the circuit at that point, you should see it on the
screen. You may have to do a little level-shifting to restore the DC level
to what the sync separator wants to see. The waveform WF1 is what the
KA2915 puts out from pin 5. Your external video should closely approximate
that waveform.
Audio is available at pin 11. If you break into the circuit there, and
switch your external audio in, you should be good to go. Level-shifting
shouldn't be needed there because it's AC coupled to the audio circuit in
the TV.

Good luck!!
Cheers!!!
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Time is what keeps everything from happening all at once.

 

[David]

If you have not already replaced the 20 or so bad electrolytic capacitors,
do so now. This is a Mitz set well known for lots of bad capacitors,
especially in the SMPS that take out the Reg ic, plus the vertical circuit
has several that are known to go bad.

All Mitz sets should get a 100% ESR check, visual check for any signs of
electrolyte on the pcb or legs, and any large values should be removed for
proper inspection.

David

<ozzyman1@sbcglobal.net> wrote in message
news:3F550ABA.9AE53356@sbcglobal.net...

Had a trapezoid small picture in the center of this 35". Couldn't find
anything wrong except
some readings from the Regulator. Replaced the STRM6511 and seemed to
correct picture
quality. Horiz. looks good, but Vert. down from top 2" and up from
bottom 2". Can the Vert.
size be adjusted from the service menu? If so, can anyone assist with
the service codes for
this model so I may access them?
T.I.A.
Jim

 

[Jerry G.]

You should first verify if the audio amp section is functioning
properly. Then verify if the sound IF, and sound detector areas are
working properly. I would not be able to tell you their physical
location in your particular model of set.

You may require some test gear to troubleshoot this. If the CRT is in
good condition, you should take the set to an experienced service place,
and have them do the job for you. These types of faults can be a
challenge even or the experienced.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
==============================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
Instruments http://www.zoom-one.com/glgtech.htm
==============================================
"Don" <dongil@wi.rr.com> wrote in message
news:Xns93EAB8A1AE2Ddongil@24.94.170.86...
Hopefully someone can help troubleshoot a problem im having with an
older
NEC Television. It's model# CT-2660A, Date of Manuf. 08/87. This has
been
an awesome TV, so im trying hard not to part with it. The problem im
having
is low sound or no sound at all. Picture quality is great, no sound. Im
also hearing kind of a low humming noise, and it depends whats on the
screen to the amount of hum noise it makes... Any Ideas?? I Removed the
control board and tested resistance on some resistors, I do have a few
bad
ones, couls this be the problem, or the result of a diffrenet problem?
Thanks in Advance.

Don

 

[Dave VanHorn]

"Tony Williams" <tonyw@ledelec.demon.co.uk> wrote in message
news:4c2bb1f311tonyw@ledelec.demon.co.uk...

In article <SaqdncbMToaQMMmiXTWJiQ@comcast.com>,
Dave VanHorn <dvanhorn@cedar.net> wrote:

if i had to guess, low voltage.

We have experienced a tv failure during an extended
browndown (and recovery). The Telefunken tv that
replaced it had a built in latching relay on the mains.

we used to live in an area with voltage as low as 70v.
i have several power strips now, with dropout relays that i wired into them.
you turn them on, then off. when the voltage droops, they kick out, and stay
there.

 

[Lew]

Resoldering the jungle IC is usually the ticket.
Lew

 

[Don]

lewisnov@aol.comnospam (Lew) wrote in news:20030902221927.10706.00000458
@mb-m29.aol.com:

Resoldering the jungle IC is usually the ticket.
Lew

Where is the jungle IC located on this model?

 

[Andy Cuffe]

Don wrote:

Hopefully someone can help troubleshoot a problem im having with an older
NEC Television. It's model# CT-2660A, Date of Manuf. 08/87. This has been
an awesome TV, so im trying hard not to part with it. The problem im having
is low sound or no sound at all. Picture quality is great, no sound. Im
also hearing kind of a low humming noise, and it depends whats on the
screen to the amount of hum noise it makes... Any Ideas?? I Removed the
control board and tested resistance on some resistors, I do have a few bad
ones, couls this be the problem, or the result of a diffrenet problem?
Thanks in Advance.

Don

I've seen lots of these with this problem caused by bad connections
between the IC pins and their sockets. The best solution is to get rid
of the sockets and solder the ICs directly to the board.
--
Andy Cuffe
baltimora@psu.edu

 

[Jerry G.]

If you are going to do service on this set, I would highly suggest to
invest in the service manual, to be able to follow up on what is going
on. The first thing to do before speculating on failed parts or a
failed IC, is to take the necessary voltage readings, and evaluate the
waveforms reaching the vertical output IC. This way you will be able to
determine if the IC is possibly defective or not.

You may find it to be more reasonable in cost to have an experienced
shop service the set for you. When buying parts, schematics, and any
necessary tools to guess at a fault condition, this can get rather
expensive for no reason. There are also strong safety issues involved
when doing TV servicing.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
==============================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
Instruments http://www.zoom-one.com/glgtech.htm
==============================================
"dino" <ebeslagic@ucdavis.edu> wrote in message
news:bj3lu6$g02$1@woodrow.ucdavis.edu...
Hi everyone,

I picked up a seemingly dead 27" JVC tv (AV-27920) and am trying my luck
in
attempting to fix it. The TV is dated May 1998. I have no prior
knowledge
of the TV's behavior before completely dying. Right now a consistant
event
takes place - when the TV is turned on, a blurry white horizontal line
appears in the center of the screen and then disappears quickly -- black
screen after that. The sound works; power supply (134 volt regulator)
checks ok. When the TV is turned off, I see a small round white circle
(around 2" in diameter) appear on the center of the screen for a brief
period of time.

I did minor troubleshooting so far however I am inexperienced with
reading
TV malfunctions. Would this symptom (horizontal line only showing up
once
at turn on time) be consistent with the guess that the vertical
deflection
IC is out?

I researched a bit on the internet about this particular series of JVC
tv's
and everyone points to LA7832 (IC for vertical deflection output). I
changed ~8 electrolytic capacitors around the vert section to see if any
change took place and I did not notice anything different. Would it be
correct to assume that this described behavior indicates a vertical
deflection IC problem?

Thank you for your help,
-dino
ebeslagic@ucdavis.edu

 

[TV Fixer1]

Sounds like the vertical circuit is dead, triggering the TV's shutdown circuit,
or at least blanking the video

 

[James Sweet]

Perhaps they had a loose neutral connection somewhere so that when a
particular appliance came on the line voltage rose.

The UK isn't wired like that, no V_rise is possible that way. Our
supply is 240v, not 120-0-120. Loads can only cause V_drops.


Ah, didn't realize this was in the UK.

 

[James Sweet]

we used to live in an area with voltage as low as 70v.
i have several power strips now, with dropout relays that i wired into
them.
you turn them on, then off. when the voltage droops, they kick out, and
stay
there.

70v? Is that on a 120v line or 240? Either way that's a big enough drop that
I would think a call to the utility would get it fixed up in short order.

 

[James Sweet]

Connecting ground to water is also not allowed for new buidings. A
separate ground pin in the earth, wired to a separate net in the home,
is what it should be. Never connected to neutral.

Where do people connect neutral to ground by design?


Thomas

In north america the netral and ground wires all connect to the same bus in
the service panel which is then grounded to a rod in the earth. Two hot
wires come in, one to each side of the panel forming two busses, between
either one and ground is 120v which is what most branch circuits are and
between the two is 240v which is used for heavier loads.

 

[Tony Williams]

In article <0GWdnWbPIt6x0ciiXTWJjA@comcast.com>,
Dave VanHorn <dvanhorn@cedar.net> wrote:

we used to live in an area with voltage as low as 70v.
i have several power strips now, with dropout relays that i wired
into them. you turn them on, then off. when the voltage droops,
they kick out, and stay there.

Our frequent browndown problems are caused by long runs of
overhead wires and squirrels. Anything with a switcher in
it is now powered off some sort of latching contactor.

--
Tony Williams.

 

[Active8]

In article <UKW4b.247032$cF.79109@rwcrnsc53>, jamessweet@hotmail.com
says...

Perhaps they had a loose neutral connection somewhere so that when a
particular appliance came on the line voltage rose.

or a 3-phase appliance with a fault on one phase causing weird stuff.

mike

 

[Active8]

In article <m4f9lvkbeqeqg2srkg0jjo4pgmcrmtaq83@4ax.com>, Jim-T@golana-
will-get-you.com says...

On Tue, 02 Sep 2003 06:27:00 GMT, "James Sweet"
jamessweet@hotmail.com> wrote:

Perhaps they had a loose neutral connection somewhere so that when a
particular appliance came on the line voltage rose.

[snip]

A very good possibility.

In 1993, while I was working in Europe, our oldest daughter was
house-sitting for us.

When we returned she told us that, when using our shower, it sometimes
felt like an electrical shock.

a friend wasb geting zapped from the shower fixtures. telco subscriber
side lines rubbing water pipes under the house. nice, eh?

brs,
mike

A little metering revealed 15VAC between the shower head and the
drain.

In Arizona "ground" is established by bonding water pipes to incoming
neutral (but not the sewer piping).

I also noticed that some lights would brighten and some would dim when
the A/C came on.

A call to the power company got us an instant temporary neutral while
they dug up the underground feed.

In our newest house I personally added local bonding between the
shower piping and the metal part of the drain before the floors were
poured.

...Jim Thompson

 

[Active8]

[snip]

I think power spikes are not a problem, any consumer equipment has
sufficient filtering built in to protect itself. Especially stuff like
TVs and puters. Surge protectors have little effect by comparison. The
house was on a big estate, so any problems would have been shared all
round.

Localized surges can happen if the power is shared with other massive
items that inductively switch out and in rapidly. Pow!

that's one of the first suspects that came to mind when i started
reading this thread. i can picture a house with crappy wiring blowing
stuff up when the washing machine's running. 5 used sets that have
possibly had the power circuits worked over and maybe a filter screwing
up or some other power prob. i'd have wanted a chart recorder on it
after the 2nd set went south. at least on a power prob like no pic/no
sound/obvious x-ray detect shut-down.

or a bad cockroach problem :-0 bunch of filthy old sets?

[snip]

Well, I had seen one once, errant loose staple inside a late model
(citizen) flat CRT combo tv/vcr kept shutdown, the SMPS is smart
design and sensitive so there wasn't a blow up at all. Took that bit
off between the magnetic biased inductor pin and ground pan. TV
started working fine.

i found a foam packing peanut in a cheap combo once. that was an easy
$25 for a gear reset and a quick check w/ lite cleaning.

Regards, NT

Cheers,

Wizard